Process of producing chloranil



PROCESS OF PRODUCING CHLORANH.

Joachim Mattner, Berlin-Charlottenburg, Germany, assignor to Schering A. G., Berlin, Germany, a corporation of Germany No Drawing. Application October 15, 1957 erial No. 690,193

the production of chloranil. More particularly, the invention concerns the production of chloranil by nitric acid treatment of the resinous by-products obtained in the production of pentachlorphenol by hydrolysis of hexachlorbenzene.

This application is a continuation-in-part of my copending application, Serial No. 539,920, filed October 11, 1955, now abandoned.

In the industrial process for the conversion of hexachlorbenzene to pentachlorphenol by saponification or hydrolysis using alkaline agents, there remain as final residues, smeary resinous by-products in substantial quantities. These residues were, prior to the present invention, regarded as completely valueless, and were discarded because no feasible and economical method of utilizing them was available. They presented moreover, a continuous disposal problem, since the presence in' them of minor amounts of materials of phenolic character, prevented their elimination by dumping into streams or sewer systems.

In accordance with the present invention, it has been found that these hitherto worthless residues may be simply and advantageously converted by treatment with nitric acid, into chloranil, and with surprisingly high yields. This is a most unexpected result, since although chloranil (tetrachloro-p-benzoquinone) may be made from pentachlorphenol by nitric acid oxidation, and is actually thus manufactured industrially, the resinous by-products which form the starting materials of the novel method of the present invention do not contain any pentachlorphenol at all other than in amounts so small that they cannot be isolated therefrom by customary technical procedures. The resinous by-products are, in fact, of unknown constitution, and I am unable to explain why they are convertible into chloranil in high yield.

I will now describe fully the manner in which smeary, resinous by-products are obtainable in the conversion of hexachlorbenzene to pentachlorphenol. This conversion method is subject to a wide range of procedural variations, which are described in detail below. It should be understood, however, that essentially similar resinous by-products are obtained regardless of the process variations employed, and that in each case, the resinous by product is capable of transformation to chloranil by my novel method.

The smeary or resinous by-products of the type which form the starting material for the method of this invention are obtained when hexachlorbenzene is saponified or hydrolyzed to pentachlorphenol by the action of an alkaline agent, generally in stoichiometric amounts. The alkaline agent may be the hydroxide of an alkali metal, such as sodium, potassium or lithium, or of an alkaline earth metal, such as calcium or barium. It may also be an alkali metal carbonate, such as sodium or potassium carbonate. The hexachlorbenzene may be reacted with the alkaline agent either in an aqueous medium, preferably With the addition of a Wetting agent or emulsifier,

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or in presence of a liquid organic solvent medium, such as, for example, a mono-, di-, or trihydric aliphatic alcohol, or a cycloaliphatic alcohol. Examples of monohydric alcohols which may be used include methanol, ethanol, propanol, isopropanol, butanol, and amyl alcohol; examples of dihydric alcohols include alkandiols containing from 2 to 6 carbon atoms, such as ethylene glycol, butandiol, or hexandiol. Other examples of alcohols which may be used include glycerol and cyclohexanol.

The hydrolysis is generally carried out by heating the hexachlorbenzene and the alkaline agent for a period of about 2 to 5 hours, at a temperature between about to 150 0, depending upon the agents and solvent media employed, until hydrolysis is complete. When utilizing the lower boiling media, the hydrolysis may be carried out under pressure, if desirable.

After the conversion to pentachlorphenol is complete, the solvent medium is removed by distillation and the reaction product, mainly sodium pentachlorphenolate, is treated with water and a mineral acid, such as hydrochloric acid or sulfuric acid, and filtered off, for example by suction. The solid product thus obtained is dissolved in a volatile organic solvent such as, for example, a halogenated aliphatic hydrocarbon, including ethylene dichloride, chloroform, or carbon tetrachloride, or an aromatic hydrocarbon, such as benzene, toluene, or xylene, or an oxygenated heterocyclic solvent such as tetrahydrofuran, and this solution is then concentrated or cooled until pentachlorphenol no longer separates out. Thereupon all the volatile organic solvent is removed from the mother liquor, as by distillation. There remains behind the smeary by-product which comprises the starting material for the novel process of this invention.

It is emphasized that the smeary by-products obtained in this Way and in accordance with the variations described below no longer contain any pentachlorphenol other than in amounts so small that it cannot be isolated by the customary technical procedures.

It will be understood that variations in the procedure for obtaining pentachlorphenol just described may be made, as for example, by removing the alcohol from the hydrolysis products by filtration instead of by distillation, or by subsequently distilling the separated alcohol and combining any distillation residue with the filtered product, but such variations have been found to have little if any influence upon the nature and characteristics of the smeary byproduct which forms the starting material of the present invention. Similarly, whether the hydrolysis of the hexachlorbenzene is carried out with an alkali metal hydroxide and methanol at about C., or with an alkali metal hydroxide and ethanol at about to C., or even at C., has no substantial effect upon the final by-procluct residue.

The by-products are essentially similar when a poly-- hydric alcohol such as glycerol is used as the solvent medium for the original hydrolysis. In such case, however, the glycerol must be thoroughly removed from the by-product residue, lest nitroglycerine be formed when the residue is converted into chloranil in accordance with my novel process.

Similar smeary by-products are obtainable when the hexachlorbenzene is converted into pentachlorphenol by means of an aqueous solution of an alkali metal hydroxide, advantageously in the presence of a Wetting agent or emulsifier at a temperature of about to 240 C. The emulsifier should be stable under the alkaline conditions, such as for example, a nonionic type, such as a polyglycol ether obtained by condensing alkylene oxides with organic hydroxy compounds of at least six Similar by-products are also obtainable when the hydrolysis of the hexachlorbenzene to pentachlorphenol is effected with an alakli metal or alkaline earth metal hydroxlde in the proportions of 1:2 or 1:3 in the presence of'an-alkandiolsolvent carrier, said alkandiol having from 2 to 6 carbon atoms, by heating .at about 150 C. without the use of pressure. As a solvent carrier of this type there may be used, for example, ethylene glycol. When the reaction is complete, the alkandiol' is removed by distillation, the residue is added to an aqueous acid solut on, stirred and filtered. The residue from the filtratron is taken up in anorganic solvent of the type mentioned previously, and pentachlorphenol is then caused to separate from this solution by concentration and cooling and filtered off. The solvent is distilled off from the filtrate, leaving the smeary by-product residue.

By-product residues of the same type are obtained when the hydrolysis of hexachlorbenzene to pentachlor phenol is carried out using either sodium carbonate, potassium carbonate, calcium hydroxide, or barium hydroxlde as the alkaline agent in the presence of a liquid alcohol solvent carrier such as ethanol at a temperature between about 150 and 200 C. The reaction mixture can be further processed by passing an acid into it in gaseous phase, such as gaseous HCl, whereupon the alkali or alkaline earth metal salt of the pentachlorphenol is transformed into free pentachlorphenol, and excess base is neutralized by formation of the corresponding chloride. The latter may be recovered by centrifuging the quantities which separate during the concentration of the pentachlorphenol solution. Upon distilling off the solvent carrier, the same type of smeary byproduct remains behind.

In accordance with the present invention, the smeary resinous by-products obtained as described above, may be transformed into remarkably pure chloranil in very high yields by treatment with nitric acid of a concentration of at least 97% in a proportion ranging from about 4.5 to 6 parts. by weight of the nitric acid to 1 part of resinous by-product being treated. Mixtures of various by-products may, of course, also be employed. The temperature of treatment should generally not exceed about 60 C., and the preferred range of temperature lies between about 5 and +10 C.

In conducting the nitric acid treatment the addition of dehydrating agents is of advantage and permits a further improvement in yield of chloranil, or a reduction in the consumption of nitric acid, or both. Examples of such dehydrating agents include phosphorus pentoxide, concentrated sulfuric acid, and the like.

The following specific examples serve to illustrate the present invention, both with regard to obtaining the resinous by-product starting materials and their transformation into chloranil, but it is to be understood that the invention is not to be considered as limited thereto.

Example 1 In an autoclave equipped with shaking means there were heated together for a period of 2 hours a mixture of'285 g. hexachlorbenzene, 100 g. NaOH, and 810 cc. methanol. The mixture was then heated for 2 additional hours at a temperature of 130-137 C., whereupon the pressure. reached about 10 atmospheres. Thereupon the mixture was cooled and the methanol distilledofi. The residue was stirred into fairly hot water,:...a cidified with HCl, andthe precipitate was filtered off, dried and dissolved in hot benzene. The solution was cooled and the separated pure pentachlorphenol removed by suction filtration. Thereafter the filtrate was further concentrated and cooled again. A further portion of somewhat impure pentachlorphenol separated out. This treatment was repeated once more but no further significant amounts of pentachlorphenol were recoverable. Thereafterno more pentachlorphenol couldbe separated from the mother liquor. All the benzene was now distilled off, and there remained a brownish-black smeary mass having a waxy consistency and an unpleasant odor. This mass was fairly soluble in benzene, toluene, chloroform, or tetrahydrofuran, but nevertheless not completely soluble. The smeary mass was partly soluble in aqueous alkali. The yield of peutachlorphenol amounted to 92%, and the quantity of smeary by-product thus obtained amounted to 18 g. The run was repeated to obtain a total of 36 g.'of by-product.

To convert the by-product to chloranil, 35 g. of the resinous by-product obtained as just described were added slowly to 150 ml.' of 98.9% HNO with stirring and cooling. Thereupon the mixture was further stirred for 5 /2 hours at 0 to 5 C. The reaction mixture was then allowed to stand at room temperature for 12 hours more. The chloranil formed was removed by suction filtration. The yield of chloranil amounted to 32g. of quite pure product.

The greater part of the nitric acid used in the foregoing proeedure may be recovered and reused.

Example 2 There is heated in a rolling type autoclave a mixture of 570 g. hexachlorbenzene, 280 g. potassium hydroxide, and 1700 ml. of 96% ethyl alcohol, for a period of 3 hours at a temperature of about l40 C. The reaction mixture is worked up further in the manner described in Example 1. The yield of pentachlorphenol is 89%, and the amount of resinous by-product is 33 g.

The 33 g. of resinous by-product is gradually and with strong stirring added to ml. of nitric acid (sp. gr. 1.51; 99%{), maintaining the temperature about '5 C. The reaction mixture is then stirred for another 7 hours, whereupon the temperature is permitted to rise slowly to +24 C. The reaction mixture is then poured'into water and the chloranil thus obtained is filtered off by suction. The yield was 24 g., the melting point after a single washing with methanol lay between 280 and 28l.5 C.

Example 3 A reaction mixture of 570 g. hexachlorbenzene, 200 g. NaOH, and 2000 ml. absolute ethanol was heated for 2 hours at 144 147 C. This reaction mixture was separated into pentachlorpheno-l and smeary by-product in accordance with theprocedure described in Example 1. The by-product was then treated with nitric acid in accordance with the procedure described in Example 2. The yield and purity of the resulting chloranil approximated that obtained in Example 2.

Example 4 For purposes of preliminary dehydration there were heated to boiling in a flask fitted with a stirrer, reflux condenser, and water trap, 129.3 g. cyclohexanol, 152.3 g. ethylene glycol, and 55 g. sodium hydroxide. About 20 g. of water were thus separated. Then another 25 g. of cyclohexanol was distilled off. At a temperature of 140 C. there was introduced in portions a total of 142.5 g. of hexachlorbenzene, the temperature meanwhile rising to about C. Before each new addition of hexachlorbenzene the temperature was again reduced to 140-145. The mixture was then brought to boiling in the course of one-half hour, kept at the boiling point for 1 hour, thereupon 40 g. of cyclohexanol were distilled off and the residue of steam distillation was made acid to Congo red with sulfuric acid, and the crude pentachlorphenol filtered by suction. This pentachlorphenol was then dissolved in hot toluene and the solution then cooled, whereupon pure pentachlorphenol separated. The toluene solution was then concentrated and again filtered by suction, whereby more pentachlorphenol, but of lower purity, separated out. No more pentachlorphenol could'be obtained from the mother liquor thus obtained. The remainder of the toluene was distilledoif, and there remained 7 g. of a brownishblack smeary mass, which was incompletely soluble in organic solvents such as benzene, acetone, and tetrahydrofuran. This smeary mass was treated with highly concentrated HNO as described in Example 2. There was obtained 4 g. of chloranil, melting at 282 C.

Example 5 In an autoclave equipped with stirrer there were heated 855 g. (3 mol) hexachlorbenzene, 300 g. NaOH, and 2.5 liters of isopropyl alcohol for 2 hours at 135 C. The isopropyl alcohol was distilled ofi. After cooling the reaction mixture was stirred into about 5 liters of hot water, HCl was added to an acid reaction, and the crude pentachlorphenol was filtered ofi. Concentration and cooling of the mother liquor yielded a further fraction of impure pentachlorphenol. Upon removal of the solventfrom the mother liquor there was obtained 34 g. of a smeary by-product. This by-product was treated with nitric acid by adding in portions to 150 cc. of 99% HNO at room temperature, stirring overnight, pouring the reaction mixture into water and filtering. There was thus obtained about 9 g. of chloranil. If instead there is used 80 cc. of a 99% HNO together with g. phosphorus pentoxide, and the mixture is similarly worked up, the yield of chloranil is almost doubled.

Example 6 The invention is also applicable to the smeary resinous mass obtainable from the refining of crude commercial pentachlorphenol. 500 g. of such crude commercial pentachlorphenol having a tn.- pt. of 135167 C. are heated with 500 cc. of a volatile organic solvent such as benzene. The mixture is coo-led, and the undissolved purified pentachlorphenol is filtered off by suction. It has a m. pt. of 180-183" C. The mother liquor thus obtained is evaporated to dryness and the benzene is recovered. The residue is a smeary, almost black mass.

35 g. of this by-product residue are added to 150 cc. of concentrated HNO (sp. gr. 1.51) at a temperature of 3 C. The mixture is stirred for 8 hours whereby the temperature is allowed to increase to 23 C. The resulting reaction mixture is poured into water and the precipitated chloranil is filtered off by suction. The yield amounts to g. After washing the chloranil once with methanol, its m. pt. is 282 C.

Example 7 A reaction mixture of 855 g. hexachlorbenzene, 390 g. potassium hydroxide, and 750 g. ethylene glycol is heated for 1 /2 hours at 170 C., cooled, and stirred into hot water. The solution is acidified to Congo red with HCl, and the resulting precipitate filtered by suction, dissolved in hot xylene, and then cooled, whereupon pure pentachlorphenol separates. The mother liquor is concentrated and cooled again, whereby a further portion of pentachlorphenol is obtained. No more pentachlorphenol is obtainable from the ino-therdiquor upon repeating this procedure. The xylene 1s evaporated to dryness, whereby there are obtained 37 g. of a resinous, smeary, almost black mass.

g. of the residue are added in portlons to 150 cc. of 98% HNO the temperature being kept at +10 C. The mixture is stirred for 7 hours at between +10 and +20 C. and the reaction mixture worked up as in Example 1. The yield of chloranil amounted to 12 g. If the by-product is treated in the same manner, but with addition to the nitric acid of 100 cc. of concentrated sulfuric acid, 16 g. of chloranil are obtained.

In the appended claims it is to be understood that the expression resinous by-product obtained in the hydrolysis of hexachlorbenzene to pentachlorphenol by means of an alkaline agent refers to the smeary, resinous by-products of unknown composition described above, and which are obtained by heating hexachlorbenzene with an alkaline agent as defined above, in the presence of a solvent medium, removing the solvent, acidifying the residue to separate crude pentachlorphenol, dissolving the crude pentachlorphenol in a volatile organic solvent, crystallizing pure pentachlorphenol therefrom until no more pentachlorphenol separates, and evaporating the volatile solvent from the mother liquor to obtain a residue which is the resinous by-product in question. Further, that the expression also includes the resinous by-product obtained in refining crude commercial pentachlorphenol by dissolving it in a volatile organic solvent, crystallizing pure pentachlorphenol therefrom, and evaporating the solvent to obtain a dark resinous residue.

The invention may be otherwise variously embodied and practiced within the scope of the following claims.

I claim:

1. Process of producing chloranil from the resinous by-product obtained in the hydrolysis of hexachlorbenzene to pentachlorphenol by means of an alkaline agent and containing no isolatable residual pentachlorphenol, which comprises treating said by-product with from about 4.5 to 6 parts by weight of nitric acid of a concentration of at least 97% at a temperature below about 60 C.

2. Process of producing chloranil from the resinous by-product obtained in the hydrolysis of hexachlorbenzene to pentachlorphenol by means of an alkaline agent and containing no isolatable residual pentachlorphenol, which comprises treating said by-product with from about 4.5 to 6 parts by weight of nitric acid of a concentration of at least 97% at a temperature between about 5 and +10 C.

3. Process of producing chloranil from the resinous by-product obtained in the hydrolysis of hexachlorbenzene to pentachlorphenol by means of an alkaline agent and containing no isolatable residual pentachlorphenol, which comprises treating said by-product with from about 4.5 to 6 parts by weight of nitric acid of about 99% concentration at a temperature not greater than about 60 C.

4. Process of producing chloranil from the resinous by-product obtained in the hydrolysis of hexachlorbenzene to pentachlorphenol by means of an alkaline agent and containing no isolatable residual pentachlorphenol, which comprises treating said by-product with from about 4.5 to 6 parts by weight of nitric acid of a concentration of at least 97% and a dehydrating agent selected from the group consisting of phosphorus pentoxide and concentrated sulfuric acid.

5. In the process of producing chloranil which comprises heating hexachlorbenzene with an alkaline agent in presence of a solvent medium, to hydrolyze the hexachlorbenzene to pentachlorphenol, removing the solvent medium, acidifying the residue with a mineral acid to liberate crude pentachlorphenol, separating and then dissolving the crude pentachlorphenol in a volatile organic solvent, and crystallizing pure pentachlorphenol therefrom until separation is complete, the improvement which comprises evaporating the volatile solvent from the mother liquor to obtain a smeary resinuous byproduct containing no isolatable residual pentachlorphenol, and treating said by-product with from about 4.5 to 6 parts by weight of nitric acid of .a concentration of at least 97% at a temperature below about 60 C.

6. Process of producing chloranil which comprises dissolving crude commercial pentachlorphenol in a volatile organic solvent, crystallizing pure pentachlorphenol therefrom, evaporating the volatile solvent from the mother liquor to obtain a smeary resinuous by-product containing no isolatable residual pentachlorphenol, and treating said by-product with from about 4.5 to 6 parts by weight of nitric acid of a concentration of at least 97% at a temperature below about 60 C.

No references cited. 

1. PROCESS OF PRODUCING CHLORANIL FROM THE RESINOUS BY-PRODUCT OBTAINED IN THE HYDROLYSIS OF HEXACHLORBENZENE TO PENTACHLORPHENOL BY MEANS OF AN ALKALINE AGENT AND CONTAINING NO ISOLATABLE RESIDUAL PENTACHLORPENOL, WHICH COMPRISES TREATING SAID BY-PRODUCT WITH FROM ABOUT 4.5 TO 6 PARTS BY WEIGHT OF NITRIC ACID OF A CONCENTRATION OF AT LEAST 97% AT A TEMPERATURE BELOW ABOUT 60*C. 